of China Australia Food Security Cooperation Initiative (CAFSCI)

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Use of inhibitors to improve the efficiency of urea as a nitrogen fertilizer

Overview of Project

Overview Objectives Although nitrogen deficiency is a major constraint to increasing the yield of food crops in Asia to feed a growing population, fertiliser nitrogen is used inefficiently, with grain crops often utilising only 20-40% of the nitrogen applied.

A previous ACIAR project (8206) showed that much of the nitrogen applied in urea fertiliser is lost to the atmosphere in the form of ammonia and dinitrogen gases. Because urea is rapidly hydrolysed to ammonia by the enzyme urease in flooded soil, various urease inhibitors have been tried in the field as means of reducing ammonia loss. While these have had mixed success, project 8206 further showed that reducing ammonia loss alone did not reduce total nitrogen loss, because the nitrogen conserved could be nitrified, and then lost by denitrification. Therefore, it is usually necessary to limit both ammonia loss by using a urease inhibitor and nitrification by using a nitrification inhibitor. This combined approach again has given mixed results in the field.

Among urease inhibitors, a naturally occurring one identified by scientists at the Fujian Academy of Agricultural Science (FAAS) has given the most promising results. When used in conjunction with a nitrification inhibitor in a field experiment at Fuzhou, it increased grain yield by 15%, and uptake of nitrogen by the grain by 6%. However, its use in other countries has not been successful.

In the current project aimed at improving the efficiency of fertiliser nitrogen and increasing grain yield, the collaborators plan first to determine the factors controlling the effectiveness of synthetic and naturally occurring inhibitors under field conditions. They will undertake laboratory and field studies to:

  • prepare larger amounts of the naturally occurring inhibitor so that it can be characterised and tested;
  • determine whether there are enzymes other than urease in flooded rice fields that can catalyse the decomposition of urea;
  • determine why the effects of current urease inhibitors are short-lived, and develop slow-release inhibitor systems so that the effectiveness of the inhibitors will be prolonged; and
  • test the influence of combinations of urease and nitrification inhibitors on rice grain yield and nitrogen recovery in the field under temperate and tropical conditions.

Scientists from FAAS and the Department of Biochemistry, University of Queensland (UQ), will study the production and characterisation of the naturally occurring inhibitor. UQ scientists will also study the enzyme urea amidolyase, which occurs in green algae and could account for significant losses of urea fertiliser in flooded rice paddies when algae are blooming. Laboratory work will be done in Australia and China.

Scientists from the CSIRO Division of Plant Industry, in collaboration with colleagues from FAAS and the Department of Agriculture (DOA), Thailand, will conduct field studies on factors affecting inhibition of urea hydrolysis and denitrification, and the effect of various combinations of urease and nitrification inhibitors on grain yield and efficiency of fertiliser nitrogen. The field work will be done in China, Thailand and Australia.

During the collaborative research, visiting scientists from FAAS will work at UQ, and visiting scientists from FAAS and DOA will work in the CSIRO Division of Plant Industry for varying periods, testing the inhibitors in both glasshouse and field.

If attempts to use urease and nitrification inhibitors in flooded rice fields are successful, nitrogen use efficiency and grain yield should increase. This would contribute substantially to Asian food supplies. It would also mean that less, expensive fertiliser would be required. Australia will benefit in the same way as the developing countries, although not to the same extent, because the country produces much less rice. Nevertheless, the inhibitors will increase the efficiency of nitrogen applied to other crops such as wheat and sugar cane.

The project will also strengthen the research capabilities of the Australian, as well as the collaborating, scientists. The latter will particularly benefit from the experience of working in the sophisticated CSIRO and University of Queensland laboratories and by working closely with experienced visiting scientists in their own countries.

Project Dates

01 Jul 1990 - On Going


Fujian Academy of Agricultural Sciences - China
Department of Agriculture - Thailand
University of Queensland - Australia
CSIRO Division of Plant Industry - Australia


Dr J.R. Freney


(02) 6247-4470

Launch Website